1. Field of the Invention
This invention relates to extruded plastic materials for covering wood or cement surfaces of boat docks and residential decks, and, more particularly, to providing such extruded plastic materials with surfaces preventing slip and fall accidents under wet conditions.
2. Background Information
Many boat docks and residential decks are comprised of a wooden floor, made of individual planks, nailed in place over a wooden framework. One problem with this type of construction arises from the fact that the upper surface of the floor is exposed to ambient conditions which cause relatively rapid deterioration of the wood. In particular, the ultraviolet rays of sunlight cause deterioration of the wood near its surface, and moisture from dew, rain, or in the case of a boat dock, from splashing, aids in the initiation of rotting. While chemical preservatives often lengthen the usefulness of the wood flooring, the wood continues to deteriorate into a condition requiring replacement. During this process of deterioration, the appearance of the wood surfaces becomes aesthetically undesirable, and the flooring may become dangerous due to splintering and even collapsing.
What is needed is a structure for covering the flooring of wood boat docks and residential decks to prevent deterioration of the wood. Such a structure would be especially useful if it could be used to cover wood flooring which has a ready been damaged by ambient exposure.
Conventional extruded flooring products, which may be made of plastic, rubber, or aluminum, have, on their upper surfaces, longitudinally extending ridges or grooves without any such features extending transversely. While this type of surface configuration is understandable considering the extrusion process by which such products are made, the result is a flooring surface which provides good traction for walking in the transverse direction, but which is found to be very slippery when a person tries to walk in the longitudinal direction. While this difference in frictional properties can be enough to cause a fall even under dry conditions, under wet conditions such flooring products can become especially dangerous.
Many dock and deck surfaces become very dangerous from the standpoint of slipping and falling when they covered by a substantial thickness of water, as during a rainstorm. Once a person's foot begins to slip, a condition of hydroplaning occurs between his foot (or the sole of his shoe) and the surface of the flooring. Under this condition, the surfaces of his foot and of the flooring do not contact one another, being instead separated by a water layer. The friction force acting between the foot and the flooring, which normally must be relied upon to prevent a fall, is now independent of the coefficient of friction of the solid materials involved, reaching a low value dependent instead on the fluid shear occurring within the water. Under such conditions, the friction force can rapidly drop to about 1/100 of its value under dry conditions. In particular, serious knee injuries occur when one foot slips in a wet area while the other foot remains stuck to the floor in an adjacent dry area, so that the knee of the foot which is not slipping is severely twisted.
What is needed is a surface for boat docks, residential decks, and the like, in which the contact surface is broken up into small sectors, so that the pressure between the foot and the contact surface is increased, reducing the chance of hydroplaning, and so that the relatively large surface areas, which are associated with the initiation of hydroplaning, are avoided. While the use of grooves and ridges extending only in the longitudinal direction in extruded flooring products performs this function to an extent, the difference in the sliding properties of such products between longitudinal and transverse directions argues against the use of such products in areas likely to become soaked with water.
3. Description of the Related Art
U.S. Pat. No. 5,009,045 describes a plastic plank member, for use with a deck arrangement, having a rigid base portion and a tread portion attached thereto, which are integrally extruded of suitable plastics. The rigid portion of the plank member is adapted to be secured to an underlying support structure. The tread portion is formed with protrusions projecting upwardly away from the tread and grooves formed therein. The characteristics of the thread result in a sufficiently high coefficient of friction to reduce the possibility of slipping on the plank member.
However, under the particularly dangerous conditions of heavy rain or splashed water, after hydroplaning is begun as part of a scenario of slipping and falling down, the coefficient of friction of the tread portion does not matter, with the frictional drag on a slipping foot being instead determined by fluid shear occurring within the water. In fact, the tread surface described in this patent includes a number of relatively large, diamond-shaped flat surfaces, surrounded by shallow ridges and grooves. In spite of the provisions made for drainage through grooves and channels, water is not rapidly drained from such surfaces, so that a fairly thick layer of water is expected to remain on these surfaces during a heavy rain.
U.S. Pat. No. 5,048,448 and U.S. Pat. No. Des. 329,914 each describe flooring material having grooves or ridges extending only longitudinally. As described in the above section, it is particularly easy to fall on such flooring because of the unexpected great difference in its frictional properties between longitudinal and transverse directions.
Therefore, what is needed is an elongated plank member having a contact surface which is broken up into small sectors, with breaks among sectors extending in both longitudinal and transverse directions, so that the pressure between the foot and the contact surface is increased, reducing the chance of hydroplaning.